The present invention relates to lubricating oils for flon compressors, compositions adapted for flon compressors and composed of a mixture of such a lubricating oil and flon, and a process for lubricating flon compressors by using such lubricating oils.
More particularly, the invention is suitably applied to cases where a flon hydrofluorocarbon containing no chlorine, for example, a hydrogen-containing flon refrigerant such as 1,1,1,2-tetrafluoroethane (HFC-134a), 1,1,2,2-tetrafluoroethene (HFC-134), 1,1-difluoroethane (HFC-152a),difluoromethane (HFC-32) or pentafluoroethane (HFC-125) (hereinafter referred to briefly as "HFC 134a, etc."), is compressed. The invention can provide particularly excellent lubricating action in these cases.
Flons having fluorine and chlorine as constituting elements, for example, chlorine-containing flons such as trichloromonofluoromethane (CFC-11), dichlorodifluoromethane (CFC-12), and monochlorodifluoromethane (HCFC-22) have been formerly used for air conditioners or car air conditioners as refrigerants. However, since environmental pollution has come to be recognized as a social problem, hydrogen-containing flon refrigerants such as HFC-134a, etc. have been highlighted as an important new type of refrigerants.
On the other hand, although a number of mineral oil-based or synthetic oil-based compounds have been known as lubricating oils for flon compressors, these compounds cannot be used for HFC-134a, etc., because the former have poor miscibility with the latter. Under the circumstances, a number of polyalkylene polyol-based compounds possessing excellent miscibility with HFC-134a have been recently proposed as lubricating oils.
For example, polyoxypropylene glycol monoalkylether having the average molecular weight of 300-1,200 (Japanese patent application Laid-open No. 1-259,093), polyoxypropylene glycol dialkylether having the average molecular weight of 300-700 (Japanese patent application Laid-open No. 1-259,094), and monoalkyl ether of polyoxyethylene polyoxypropylene copolymer (Japanese patent application Laid-open No. 55-58,298, Japanese patent publication No. 61-52,880 and Japanese patent application Laid-open No. 1-259,095) are known. Further, a number of compounds or compositions, for example, specific polyalkylene glycol monoalkyl ether (Japanese patent application Laid-open No. 2-84,491), polyalkylene glycol derivatives, such as those of dimethyl ethers in which hydroxyl groups at opposite terminals of polyalkylene glycol are methyletherified (Japanese patent application Laid-open No. 2-305,893), refrigerator-lubricating oils containing specific polyether polyols having the average molecular weight of 400 to 5,000 and specific esters (U.S. Pat. No. 4,851,144), and refrigerator compositions composed of random polyoxyalkylene glycol (Japanese patent application Laid-open No. 3-103,496, Japanese patent application Laid-open No. 3-103,497 and U.S. Pat. No. 4,971,712) are proposed.
Although currently known polyalkylene polyol-based refrigerator-lubricating oils exhibit excellent miscibility in use together with HFC-134a, etc., it cannot be said that they also exhibit satisfactory lubricating action in this case. Therefore, improvement of performance of these lubricating oils has been desired.